The nematic liquid crystal molecules structure and viscosity relationship was studied and a BPNN-QSAR model about them was established

Abstract

The nematic liquid crystal materials designed for optics, microwave communication tuning, etc. require high response speed which is correlated with the rotational viscosity and the birefringent index of the liquid crystal. In order to achieve a wide tuning range of phase modulation, the nematic liquid crystals often employ large π-electron conjugated systems and large polar groups to enhance the birefringence and dielectric anisotropy of the liquid crystal molecules. However, it increases the viscosity of the liquid crystal materials, deteriorating the response speed of the microwave devices. Here, we explore the viscosity of the nematic liquid crystal from a perspective of liquid crystal compound structure by testing the viscosity of forty-two different nematic liquid crystals designed and synthesized by us with a rotating rheometer at 25 ℃. To the best of our knowledge, the BPNN-QSAR quantitative conformation model between nematic liquid crystal molecular structure and viscosity was established for the first time. The correlation coefficient between the predicted value and the experiment value was <i>q</i>²=0.607>0.5, indicating that the model can be used to predict the viscosity performance of liquid crystal compounds. Besides, the molecular structure descriptors affecting the viscosity properties are explored. Based on the practical application and this model, seven liquid crystal molecules of two series with l large birefringent index are designed and tested, where the viscosities predicted by the BPNN model are smaller than the molecules of the same type and matched with the measured viscosities.